FIG. 1 represents a simplified target tracking system 10 which tracks a target, illustrated as being an orbiting space object, such as a satellite 12, by the use of a sensor, such as a radar system 14. Those skilled in the art of tracking know that the word “target” refers to an object being tracked, and the target may be any object or vehicle, moving or stationary, such as an automobile, an aircraft, a ship, a submarine, a spacecraft, or even a person. Radar system 14 includes a radar antenna 14a, which transmits and receives radar signals illustrated by “lightning bolt” symbols 18. Portions of the transmitted signals 18 are reflected by target 12 and return to the radar antenna 14a. The returned signals allow the generation of measurements at an output port 14o of radar system 14. These measurements include values of at least some components of target position, possibly in the form of range and angles from the radar system 14. A track is generated from these measurements locally and consists of a track state, which may include, for example, course (direction of motion), speed, acceleration, and target type. This track is applied from radar system 14 by way of a transmission path 15 to a processing arrangement 22. A further radar system 16 at a different location includes an antenna 16a, which transmits and receives radar signals illustrated by “lightning bolt” symbols 20. Portions of the transmitted signals 20 are reflected by target 12, and return to antenna 16a. The returned signals allow the generation of measurements at an output port 16o of radar system 16. These measurements include values of at least some components of target position, possibly in the form of range and angles from the radar system 16. A track is generated from these measurements locally and consists a track state, which may include course (direction of motion), speed, acceleration, and target type. This track is applied from radar system 16 by way of a transmission path 17 to processing arrangement 22. Processing arrangement 22 receives the tracks relating to the target 12 and determines from these tracks the combined track of the target. The estimated position of the target, and possibly other information, is provided to a utilization apparatus or user, illustrated in this case as being a radar display 24. The operator (or possibly automated decision making equipment) can make decisions as to actions to be taken in response to the displayed information, including location information. It should be understood that the radar tracking system 10 of FIG. 1 is only one embodiment of a general class of estimation systems which may include controlling nuclear, chemical, or manufacturing factories or facilities, control processes subject to external parameter changes, attitude control of a space station subject to vibrations, traction control of an automobile subject to weather conditions, and the like.
It often happens in arrangements such as that of FIG. 1 that the bandwidths of the transmission paths 15 and 17 are limited, and there are multiple users of the limited bandwidth, so that the bandwidth available to any one user is also limited. Multiple sensors are often used to track a dynamic process from start to finish. An example of such tracking is the tracking of a target (man-made or natural) by radars or other sensors situated in geographically dispersed locations. Such a scenario would be commonplace in a land, water, air, or space situation. The radars or other sensors may report at the same time, or the reports may be interleaved, delayed, out-of-sequence, or refer to different portions of the trajectory of the target.